In wireless transmission, methods for improving sector throughput by using multiple antennas have been researched.
The methods that use multiple antennas include a smart antenna method, a diversity method, and a spatial multiplexing (SM) method, as examples. The smart antenna method acquires a plurality of gain forming antenna beams for transmitting/receiving a signal with a high signal to noise ratio (SNR). The diversity method that uses multiple antennas decreases receiving probability of a signal having a low SNR by multiplexing signal paths when channel correlation is low so as to obtain a gain. In addition, the SM method obtains a multiplexing gain by transmitting a different signal to each of a plurality of antennas when the SNR is high.
For transmission of a radio signal, the base station uses various methods such as a direction of arrival (DOA) beamforming method using multiple antennas and a minimum mean square error (MMSE) method for avoiding another user's interference. However, when the terminal transmits a radio signal, the terminal typically uses one transmitting antenna due to increasing size and power consumption of the terminal.
Considering the contemporary standardization trends, an SM transmission method that uses multiple transmission antennas and a space time coded transmit diversity (STTD) method have been proposed for radio signal transmission to an uplink. In addition, a method for increasing an SNR by forming transmission beams in multiple antennas has been researched. A space division multiple access (SDMA) method in which a plurality of terminals transmit an uplink signal to one base station by sharing resources is an example of this method. The SDMA method may be applied to a plurality of terminals that respective include one transmission antenna or a terminal including two or more transmission antennas.
As described, transmission beamforming by using multiple antennas is needed for increasing sector capacity in the SM method, the SDMA method, and a single input single output (SISO) method. However, there is a problem of increasing power consumption of a terminal when the uplink signal is transmitted by using the multiple antennas.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.